Revolving Credit Facility and Long-Term Debt - Additional Information (Detail) - Agreement [Member] - USD ($)	1 Months Ended		3 Months Ended
	May 31, 2020	Jun. 30, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	May 30, 2020	Dec. 31, 2019	Aug. 06, 2019	Aug. 05, 2019
Line of Credit Facility [Line Items]
Credit facility borrowing used						$ 5,800,000
Line of credit facility commitment fee description						The Agreement also provides for an unused commitment fee of 0.375% per year on the average daily unused amount of the revolving credit line, as well as a fee of 1.75% of the face amount of each letter of credit reserved under the line of credit.
Outstanding balance on term loan and revolving credit facility						$ 0		$ 0
Ratio of restricted and unrestricted cash and investments to workers' compensation and safety incentive liabilities						100.00%
Maximum amount to redeem retire repurchase or acquire stock upon agreement						$ 15,000,000
Scenario Forecast [Member]
Line of Credit Facility [Line Items]
Ratio of restricted and unrestricted cash and investments to workers' compensation and safety incentive liabilities			100.00%	100.00%	100.00%
Minimum [Member]
Line of Credit Facility [Line Items]
EBITDA						30,000,000
Minimum [Member] | Scenario Forecast [Member]
Line of Credit Facility [Line Items]
EBITDA			$ 30,000,000	$ 30,000,000	$ 30,000,000
Maximum [Member]
Line of Credit Facility [Line Items]
Prohibition on incurring additional indebtedness without the prior approval of the Bank in purchase money financing						$ 1,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity									$ 33,000,000	$ 28,000,000
Credit facility, expiration date						Jul. 01, 2022
Unused commitment fee on unused amount during period						0.375%
Revolving Credit Facility [Member] | Scenario Forecast [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity	$ 50,000,000						$ 33,000,000
Credit facility, expiration date	Jul. 31, 2021
Revolving Credit Facility [Member] | Daily Floating Rate [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description						the daily floating rate of one-month LIBOR plus 1.75% or (b) the fixed rate of LIBOR plus 1.75%
LIBOR plus rate						1.75%
Revolving Credit Facility [Member] | Fixed Rate [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description						the fixed rate of LIBOR plus 1.75%
LIBOR plus rate						1.75%
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity									$ 8,000,000	$ 7,500,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Unused commitment fee on unused amount						1.75%
Chubb Letter of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity						$ 63,700,000
Credit facility, expiration date						Jul. 01, 2020
Percentage of initial fee under letter of credit		2.50%				2.50%
Percentage of aggregate fee under letter of credit						95.00%
Percentage of annual fee under letter of credit						1.00%
Chubb Letter of Credit [Member] | Collateral Accounts [Member]
Line of Credit Facility [Line Items]
Percentage of deposit in collateral accounts						50.00%
Deposit in collateral accounts						$ 32,400,000
Chubb Letter of Credit [Member] | Collateral Accounts [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Deposit in collateral accounts						$ 16,000,000
Term Loan [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description						one-month LIBOR plus 2.0%
Term loan with principal bank						$ 3,900,000		$ 4,000,000
Payment of monthly principal of term loan						$ 18,375
Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
LIBOR plus rate						2.00%